[PATCH AUTOSEL 4.19 207/209] powerpc/time: Fix clockevent_decrementer initalisation for PR KVM

Sasha Levin
2019-11-13T02:17:21Z

From: Michael Ellerman <mpe@ellerman.id.au>

[ Upstream commit b4d16ab58c41ff0125822464bdff074cebd0fe47 ]

In the recent commit 8b78fdb045de ("powerpc/time: Use
clockevents_register_device(), fixing an issue with large
decrementer") we changed the way we initialise the decrementer
clockevent(s).

We no longer initialise the mult & shift values of
decrementer_clockevent itself.

This has the effect of breaking PR KVM, because it uses those values
in kvmppc_emulate_dec(). The symptom is guest kernels spin forever
mid-way through boot.

For now fix it by assigning back to decrementer_clockevent the mult
and shift values.

Fixes: 8b78fdb045de ("powerpc/time: Use clockevents_register_device(), fixing an issue with large decrementer")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/kernel/time.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 6a1f0a084ca35..7707990c4c169 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -988,6 +988,10 @@ static void register_decrementer_clockevent(int cpu)

printk_once(KERN_DEBUG "clockevent: %s mult[%x] shift[%d] cpu[%d]\n",
dec->name, dec->mult, dec->shift, cpu);
+
+ /* Set values for KVM, see kvm_emulate_dec() */
+ decrementer_clockevent.mult = dec->mult;
+ decrementer_clockevent.shift = dec->shift;
}

static void enable_large_decrementer(void)
--
2.20.1